SIMULTANEOUS MEASUREMENTS OF HEAT, WATER-VAPOR AND CO2 FLUXES ABOVE ALFALFA AND MAIZE

The objective of this study was to measure the short-term biophysical responses of alfalfa and maize crops growing in unmodified field environments. Flux densities of heat (H), water vapour (LE) and CO2 (Fc) between the crop surface and the atmosphere were obtained using a Bowen ratio-energy balance (BREB) method. Two BREB systems were designed and used to provide simultaneously the fluxes above adjacent fields of unirrigated alfalfa (Medicago saliva L.) and maize (Zea mays L.) in southern Ontario (Koppen's climate classification Dfb). Differences in fluxes between alfalfa and maize were characteristic of their C3 and C4 metabolism, respectively, as indicated by higher rates of Fc above maize, higher rates of LE above alfalfa and chilling sensitivity in maize, but not alfalfa. Bowen ratios were larger above the alfalfa crop following harvest, but were highest for maize when both crops were fully grown. © 1990.